Genesis and nature of ore-forming fluids in the Senjedeh gold mine, Central Iran; using microthermometry study

Senjedeh gold mine is located 60 km southwest of Delijan in the central part of the Sanandaj-Sirjan zone (SSZ). This is one of the active mines of the Muteh mineral area. The gold mineralization in the study area occurred as quartz- sulfide veins and veinlets along N40W tending, NE dipping normal faults in metarhyolite host rock. The most important hydrothermal alteration types are sericitization, kaolinitization, silicification and sulfidization, which silicified and sulfide alterations are developed in the inner parts of the fault zones adjacent to the mineralized zones. Five group of fluid inclusion can be identified based on fluid inclusion petrography in Senjedeh, which main primary fluid inclusion is the two-phase fluid (L + V) with dominant phases of (H2O) and (CO2). Evidences from fluid inclusion microthermometry studies indicate the contribution of CO2 bearing ore-forming fluids. They are characterized by the mean homogenization temperature of 300oC, and average salinity of 11 % wt NaCl. They are genetically linked to the generation of metamorphic fluids that are typically characterized by low salinity and mixed H2O–CO2 compositions. Results from petrography, temperature and fluid inclusion homogenization (homogenization to fluid) indicate that released fluids during progressive metamorphism have been mixed with magmatic fluids and meteoritic water, which penetrateed up to a few kilometers through faults. These processes are responsible for alteration and mineralization along normal faults. Based on the evidences of geology, alteration and microthermometry, and comparing with Iran and world's gold deposits, this mine can be considered as an orogenic gold mineralization.